Cr Oscillation Circuit and Electronic Device
a technology of oscillator circuit and oscillator frequency, which is applied in the direction of pulse generation by logic circuit, pulse technique, electronic switching, etc., can solve the problem of large error between the desired oscillation frequency set and the actual oscillation frequency, and achieve the effect of reducing the selection margin
Inactive Publication Date: 2008-01-10
ROHM CO LTD
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Benefits of technology
[0006] The present invention has been made in view of these problems and an object thereof is to provide a CR oscillator circuit and an electronic apparatus that broaden the selection margin for means for adjusting the oscillation frequency.
[0008] By setting the above-described relationship in the CR oscillator circuit, the upper bound of a ratio by which the capacitance value of a CR oscillator circuit as a whole is reduced can be lower than the upper bound of a ratio by which the resistance value of a CR oscillator circuit as a whole. In other words, the oscillation frequency can be adjusted to a frequency lower than that obtained before the capacitance value of a CR oscillator circuit as a whole is reduced in a manner that the resistance value of a CR oscillator circuit as a whole is increased at least from RMIN to RMAX maximally even when the capacitance value of a CR oscillator circuit as a whole is reduced maximally from CMAX to CMIN. According to this embodiment, for example, when the oscillation frequency is adjusted low, the adjustment can be accomplished by employing not only a method in which the resistance value is merely increased but also a method in which the capacitance value is reduced and at the same time the resistance value is increased. Hence, the selection margin for means for adjusting the oscillation frequency can be broadened.
Problems solved by technology
On account of the fact that variation in each element of inverters, capacitors and resistors is large in the conventional CR oscillator circuit, there is a case where the error between the desired oscillation frequency set and the actual oscillation frequency is large.
Method used
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Embodiment Construction
[0021]FIG. 1 shows a structure of an electronic apparatus 10 according to an embodiment. The electronic apparatus (electronic device) 10 includes a bandgap regulator 112, a voltage control circuit 110, a CR oscillator circuit (CR oscillation circuit) 100 and a control unit 120. This electronic apparatus 10 is installed in electronic equipment such as household electric appliances or video equipment, and an internal CR oscillator circuit 100 produces a drive signal OUT to drive a LCD (Liquid Crystal Display) panel, not shown.
[0022] The bandgap regulator 112 receives the power from a supply voltage Vcc and outputs a voltage of a predetermined fixed voltage Vc, for example, 1.2 V. The voltage control circuit 110 is provided between the bandgap regulator 112 and the CR oscillator circuit 100, inputs the fixed voltage Vc from the bandgap regulator 112 and supplies a predetermined supply voltage Va to the CR oscillator circuit 100. The voltage control circuit 110 includes a group of two ...
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It is preferable to increase the selection scope of oscillation frequency adjustment means. In a CR oscillation circuit, a first oscillation capacitor and a second oscillation capacitor are arranged in parallel so that a capacity value of the entire CR oscillation circuit can be selected. A plurality of resistors including at least one variable resistor such a fifth trimming resistor are arranged in series, so that the resistance value of the entire CR oscillation circuit can be selected by adjusting the resistance value of the fifth trimming resistor. The minimum value CMIN and the maximum value CMAX which can be selected as a capacitance value of the entire CR oscillation circuit and the minimum value RMIN and the maximum value RMAX which can be selected as a resistance value of the entire CR oscillation circuit are in the relationship as follows: CMIN RMAX≧CMAX RMIN.
Description
TECHNICAL FIELD [0001] This invention relates to a CR oscillator circuit used for various electronic circuits or the like and an electronic apparatus having said oscillator circuit. BACKGROUND TECHNOLOGY [0002] In electronic circuits such as microcomputers mounted on electronic equipment like household electric appliances or video equipment, there are many cases where the oscillator circuit for mainly producing the reference frequency is provided. As examples for this oscillator circuit, known are the crystal / ceramic oscillator circuit using crystal oscillator and ceramic resonator and the CR oscillator circuit using resistors and capacitors. [0003] Normally, the oscillation frequency in a CR oscillator circuit is determined by the characteristics of inverters and each value of capacitors and resistors. In Patent Document 1, a technology is disclosed in which a capacitor is further provided between the input terminal and the ground in the first-stage inverter and the variation in po...
Claims
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Login to View More IPC IPC(8): H03K3/354H03K3/00
CPCH03K3/00H03K17/00H03K3/0315H03K3/03
InventorNAKASHIMA, TAKAYUKI
OwnerROHM CO LTD